LTE Release 13 standardized concept supports the transmission of CSI (Channel State Information) measurements, based on so-called CSI Processes (see 3GPP TS 36.213 v 12.6.0), each CSI process including a NZP (Non-Zero Power) CSI-RS (CSI Reference Signal) transmission and one or more CSI-RS ZP (Zero Power) transmissions. Based on these CSI-RS signals transmitted by the eNB (base station in LTE), an UE (User Equipment) can assess the CQI (Channel Quality Indicator) including the recommended modulation and coding scheme; RI (rank indicator) or PMI (pre-coding matrix indicator) can be also included in the CSI Report.
Given the fact that, in deployments with multiple base stations, a CQI Report is needed for each combination of the transmitting base stations, the CQI approach conducts to numerous resources allocated for CSI-RS ZP. As shown in the 3GPP RAN3 contribution R3-150723, in case of coordinated CSI measurements for determining CQI in only 5 cells, the overhead of CSI-RS ZP would result in a capacity loss of 33%.
Some research papers present the notion of a network graph, presenting the path losses of the wireless connections between different nodes as a characterization of the wireless network interactions.
However, as shown above, in case of multiple interfering sources, CQI is not a suitable parameter to be used in a network graph.